Despite recent advances in tissue engineering, ischemia related to cardiovascular disease results in the death of approximately 500,000 patients per year in the case of myocardial infarction (MI) and greater than 100,000 amputations per year in the case of peripheral artery disease (PAD) in the US alone. Therefore, our long-term goal is the development of new, minimally invasive tissue-engineered therapies for the treatment of myocardial and critical limb ischemia. For MI, materials have been injected with cells in order to increase cell retention and survival, or alone to increase endogenous cell migration into the infarct area, including neovascularization, to thicken and support the left ventricular (LV) wall, or both. In the case of PAD and critical limb ischemia, very few biomaterials have been examined, and to date, they have only been studied for improving growth factor and cell delivery. No current materials meet all of the requirements of an ideal scaffold for either application, namely the ability to promote neovascularization to reduce the ischemic environment, to promote cell adhesion, survival, and maturation of endogenous or exogenously added cells, and to be injectable. Moreover, none adequately mimic the biochemical cues, which are inherent to the native extracellular matrix (ECM) that they are intended to replace. Our lab has generated injectable, tissue specific ECM hydrogels, which we show have the potential to meet all of the requirements of an ideal scaffold. These injectable materials resemble the in vivo cardiac and skeletal muscle extracellular milieu in that they contain a complex assortment of the native biochemical cues found in cardiac or skeletal muscle ECM, respectively. We have shown that both materials have the potential to recruit endogenous cells to promote vascularization. Furthermore, injection of the myocardial matrix in a MI model preserves cardiac function and LV geometry, while injection of the skeletal muscle matrix enhances the recruitment and proliferation of muscle progenitors in a hindlimb ischemia model. In addition, we show in vitro studies that these materials promote muscle progenitor maturation. We hypothesize that ECM based hydrogels, which are derived from native muscle ECM and contain complex, tissue specific biochemical cues, can be delivered alone to increase endogenous cell recruitment or with exogenous cells to improve cell survival and maturation, thereby providing effective therapies for MI and severe PAD. This application will address the following specific aims: 1) To determine the influence of an injectable acellular myocardial matrix hydrogen alone on post-myocardial infarction negative left ventricular remodeling, endogenous cardiomyocyte survival, cell infiltration, and cardiac function, 2) To determine the influence of an injectable acellular skeletal muscle matrix hydrogel alone on cell apoptosis and infiltration, neovascularization, and perfusion in a hindlimb ischemia model, and 3) To determine the effects of exogenous muscle progenitors in the milieu of injectable muscle ECM derived hydrogels on neovascularization, and cell transplant retention, survival, and maturation.